Transducer sealing



March 10, 1959 G. c. TIBBETTS 2,877,362

TRANSDUCER SEALING Filed oct. 29, 1954 2 Sheets-Sheet 1 ff I J y w W Gear C. a' eff/5 A 3 *M March 10, 1959 G. c. TIBBETTS 2,877,362

TRANSDUCER SEALING Filed 0G15. 29, 1954 2 Sheets-Sheet 2 United States Patent O 2,817,362 imANsnUcER SEALING George C. Tibbetts,

Laboratories, Maine Camden, Maine,

assignor to Tibbetts Inc., Camden,

Maine, a corporation of This invention relates to transducers of the type comprising an electrostrictive, piezoelectric or other slab which changes dimensions between two points in response to electrical forces, for use in converting electrical energy into mechanical vibrations or vice versa, and more particularly transducers of the type disclosed in my Patent 2,403,692 which comprise a diaphragm or other arched toggle member connected to the Slab at spaced points so as to vibrate in response to the aforesaid changes of dimensions.

As is well known the aforesaid slabs are often susceptive to change of moisture content and the objects of the present invention are to produce a transducer in which the slab is protected from loss or gain of moisture, which is simple and economical in construction, which is durable and reliable in use, and which at the same time has high sensitivity and excellent performance.

In one aspect the present invention consists in covering the major surface of one or both sides of the slabs with metal foil or other moisture resistant material to impede transfer of moisture to or from the slab independently of electrodes, diaphragms or other slab covering. When employing electrodes the material is applied over the electrodes.

moisture resistant layer and slab, with moisture resistant material sealing the aforesaid layer to the flange.

When a diaphragm or other flexible sheet is applied to each side of the slab, whether it be a single slab or a composite slab, preferably the peripheral portions of the flanges of the two sheets are opposed to each other and the space therebetween is filled with the aforesaid sealing material.

For the purpose of illustration typical embodiments of the invention are shown in the accompanying drawings in which Figs. 1 and 2 are elevations viewed from the upper corners of Fig. 3 respectively as indicated by the arrows 1 and 2 in Fig. 3;

Fig. 3 is a plan view with a part broken away;

Fig. 4 is a section on line 4-4 of Fig. 3;

Fig. 5 is a section on line 5 5 of Fig. 3;

Figs. 6 and 7 are views like 1 and 2 of a modification;

Fig. 8 is a plan View of the modification with a part broken away;

Fig. 9 is a section on line 9 9 of Fig. 8; and

Fig. l is a section on line 10-10 of Fig. 8.

The particular embodiment illustrated in Figs. l to comprise two square piezoelectric slabs 1 and 2, electrodes 3, 4, 5 and 6 fast to the sides of the slabs respectively, layers 7 and 8 of moisture resistant material mounted over the outer electrodes 3 and 6, diaphragms 9 and 10 and leads 11 and 12. The slabs 1 and 2 are oriented so that the electrodes polarity when the composite slab is mechanically stressed by the diaphragms 9 and 10. The electrodes may be formed of any thin conducting material such as gold foil. As shown in Fig. 4 the lead 11 is secured in face contact to the electrode 3 and as shown in Fig. 5 the electrode 3 is electrically connected with the electrode 6 by means oi a jumper 13. The lead 12 is mounted between the two electrodes 4 and 5 and is provided with an insulating bushing 14 at the location where it emerges from the interior of the device.

According to the present invention the layers 7 and 8 are formed of metal foil or other moisture resistant material and the spaces between the layers and the diaphragms are sealed. Preferably the sealing material is moisture resistant adhesive and the various layers and slabs are cemented together with similar adhesive.

While the moisture resistant layers 7 and 8 may be made of organic plastic or resin, they are preferably made of thin metal having a low Youngs modulus of elasticity in order to minimize the reduction in slab sensitivity due to the fact that they must expand and contact with the slab. Aluminum foil 0.00025 thick has been found to be highly satisfactory. By using water resistant adhesive to attach the foil, any pin holes which happen to occur in the foil are sealed.

As shown in Figs. 4 and 5 the electrodes 3 and 6 are preferably somewhat smaller than the slabs, so that their peripheries are located somewhat inside the peripheries of the slabs, and the moisture resistant layers 7 and 8 preferably extend outwardly to the periphery of the slab.

As in the aforesaid patent each of the diaphragms is arched outwardly along one diagonal and inwardly along the other diagonal. Thus the corners 23 are spaced away from the slabs farther than the corners 24, the center of each diaphragm being spaced from the slabs a distance equal to the average of the distances at the high and low corners.

According to the present invention each diaphragm has a peripheral ilange comprising a portion 26 which extends transversely of the slab toward the peripheral portion of the moisture resistant layer, a portion 27 extending outwardly beyond the peripheries of the layer and slab, a portion 28 extending transversely in spaced relation to said peripheries and a portion 29 extending outwardly in juxtaposition to a corresponding portion on the other diaphragm. The space between portions 29 is filled with moisture resistant cement. The spaces 17 and 18 are usually vented to the external atmosphere by tubes 35 to prevent static pressure differences on the diaphragms 9 and 10 due to changes in atmospheric pressure. the paths through the cement 15 from the exterior of the device and from spaces 17 and 18 to the slabs 1 and 2 are long and thin, thereby impeding the transfer of mois- 3 and 6 have the same spaced differently in order to reduce the overall dimensions of the device. As in the first embodiment each diaphragm has a ange comprising a portion 26 extending toward the slab, a portion 27 extending outwardly beyond the periphery of the slab and a portion 28 extending transversely past the peripheries of the slab and covering layers. However the outturned portions 29 of the flanges are omitted and the transverse portions 28 overlap in spaced relationship. By providing the insulation layers 32 and 33 there is no danger of short circuiting the two electrodes 3 and 6 by contact between the layers 7 and 8 and` the diaphragms when both the moisture resistant layers and the diaphragms are made of metal.

It should be understood that the present disclosure is for the purpose of illustration only and that this invention includes all modications and equivalents which fall within the scope of the appended claims.

I claim:

1. A device of the character referred to comprising a slab which changes dimensions between two points in response to electrical forces, a layer of moisture resistant material over the major portion of one side of the slab, and a exible sheet extending across said side of the slab in spaced relation thereto, the sheet being anchored to the slab at said points and being arched transversely of a line joining the points so as to be fixed by said changes of dimension, said layer having a peripheral portion and said sheet having a peripheral iiange which extends transversely of the slab toward said peripheral portion, thence outwardly beyond said peripheral portion and thence transversely in spaced relation to the edges of the layer and slab, and moisture resistant material sealing said layer to said flange.

2. A device of the character referred to comprising a slab which changes dimensions between two points in response to electrical forces, a layer of moisture resistant metal foil over the major portion of one side of the slab, and a liexible sheet extending across said side of the slab in spaced relation thereto, the sheet being anchored to the slab at said points and being arched transversely of a line joining the points yso as to be flexed by said changes of dimension, said layer having a peripheral portion and said sheet having a peripheral flange which extends transversely of the slab toward said peripheral portion, thence outwardly beyond said peripheral portion and thence transversely in spaced relation to the edges of the layer and slab, and moisture resistant material sealing said layer to said ange.

3. A device of the character referred to comprising a slab which changes dimensions between two points in response to electrical forces, a thin layer of conducting material fast to one side of the slab, over said layer a layer of insulation, over said layers a layer of moisture resistant material, a flexible sheet extending across said side of the slab in spaced relation thereto, the sheet being anchored to the slab at said points and being arched transversely of a line joining the points so as to be flexed by said changes of dimension, said moisture resistant layer having a peripheral portion and said sheet having a peripheral ilange which extends transversely of the slab toward said peripheral portion, thence outwardly beyond said peripheral portion of said layers and thence transversely in spaced relation to the edges of said layers, and moisture resistant material sealing said moisture resistant layer to said flange.

4. A device of the character referred to comprising a slab which changes dimensions between two points in response to electrical forces, a thin layer of conducting material fast to one side of the slab, over said layer a layer of insulation, over said layers a layer of metal foil over the major portion of said side, a liexible sheet extending across said side of the slab in spaced relation thereto, the sheet being anchored to the slab at said points and being arched transversely of a line joining the points so as to be flexed by said changes of dimension, said foil layer having a peripheral portion and said sheet having a peripheral flange which extends transversely of the slab toward said peripheral portion, thence outwardly beyond the edges of said layers and thence transversely in spaced relation to the edges of said layers, and moist-ure resistant material sealing said foil layer to said ange.

5. A device according to claim 1 in which the device is similarly constructed on the other side of the slab.

6. A device according to claim 5 further characterized in that the peripheral portions of the anges of the two flexible sheets are opposed to each other with sealing material in the space therebetween.

References Cited in the ijle of this patent UNTTED STATES PATENTS 

